A microbe is ingested and broken into fragments by an antigen-presenting cell (APC).Which of the following would you expect to occur?

Question

Quizplus · Accepted Answer

When an APC breaks down and presents a foreign antigen, it will display small fragments of the antigen on its surface in association with major histocompatibility complex (MHC) molecules. T cells, which are responsible for cell-mediated immunity, will bind to these antigen-MHC complexes on the surface of the APC via their T-cell receptors (TCRs). This interaction will activate the T cells to differentiate into effector T cells, which can directly attack infected cells or provide help to other cells of the immune system. Therefore, choice D is the correct answer. B cells, which are responsible for humoral immunity, will usually bind to whole antigens and their fragments in the fluid environment and differentiate into plasma cells, which secrete antibodies that specifically recognize and neutralize the antigens. However, they can also release cytokines to activate T cells, so choice B is not entirely wrong. Choice A is incorrect because only T cells have TCRs, while B cells have B-cell receptors (BCRs) that recognize antigens outside of the APC. Choice C is also incorrect because plasma cells are effector B cells that secrete antibodies, not cytokines that activate APCs.

A Microbe Is Ingested and Broken into Fragments by an Antigen-Presenting